Ferrite magnet powder and magnet using said magnet powder, and method for preparing them

ABSTRACT

An La—Co ferrite magnet powder, in which Sr and Fe are replaced with La and Co, respectively, is made by carrying out a calcination process at a temperature higher than 1300° C. and equal to or lower than 1450° C. Fe has a magnetic moment oriented upwardly with respect to a crystal c-axis at a number of sites thereof, and also has an opposite magnetic moment oriented downwardly with respect to the crystal c-axis at another number of sites thereof. And Fe is replaced with Co at the greater number of sites thereof. As a result, high coercivity is attained. In this manner, coercivity can be increased while suppressing decrease in saturation magnetization σ s .

TECHNICAL FIELD

The present invention relates to ferrite magnet powder, magnet made fromthe magnet powder and methods for making the powder and the magnet.

BACKGROUND ART

Ferrite is a generic term for various compounds containing an oxide of adivalent anionic metal and trivalent iron and has found a wide varietyof applications in motors, electric generators, and so on. Typicalmaterials for a ferrite magnet include Sr or Ba ferrites with amagnetoplumbite hexagonal structure (SrFe₁₂O₁₉ or BaFe₁₂O₁₉). Each ofthese ferrites can be made from iron oxide and a carbonate of strontium(Sr) or barium (Ba) at a relatively low cost by a powder metallurgicalprocess.

A basic composition of a magnetoplumbite ferrite is usually representedby a chemical formula of MO.nFe₂O₃, where M is a metal element to bedivalent anions and is selected from the group consisting of Sr, Ba, Pband so on. In the ferrite, iron ions (Fe³⁺) located at respective siteshave spin magnetic moments and are bonded together by superexchangeinteraction with oxygen ions (O⁻²) interposed therebetween. At each ofthese sites, Fe³⁺ has an “upward”or “downward” magnetic moment withrespect to the c-axis. Since the number of sites with the “upward”magnetic moment is different from that of sites with the “downward”magnetic moment, the, ferrite crystal exhibits ferromagnetism as a whole(and is, called a “ferrimagnetism”).

It is known that the remanence B_(r), which is one of the indicesrepresenting the magnetic properties of a magnetoplumbite ferritemagnet, can be improved by enhancing I_(s) of the crystal or increasingthe density of a ferrite sintered compact and aligning the orientationsof the crystal more fully. It is also known that the coercivity H_(CJ)of a ferrite magnet can be enhanced by increasing the fraction of singledomain crystals existing in the magnet. However, if the density of thesintered compact is increased to improve the remanence B_(r), then theferrite crystals grow at a higher rate, thus decreasing the coercivityH_(CJ). Conversely, if the grain sizes are controlled with the additionof Al₂O₃, for example, to increase the coercivity, then the density ofthe sintered compact decreases, resulting in decrease of the remanence.Compositions, additives and production conditions for ferrites have beenresearched and developed from various angles to improve these magneticproperties of a ferrite magnet. However, it has been difficult todevelop a ferrite magnet with its remanence and coercivity bothimproved.

The present applicant developed a ferrite magnet with the coercivityimproved by adding Co to the source material and without decreasing theremanence thereof (see Japanese Patent Gazette for Opposition Nos.4-40843 and 5-42128).

After that, a ferrite magnet with the saturation magnetization σ_(s)improved by replacing Fe and Sr with Zn and La, respectively, wasproposed (see Japanese Laid-Open Publication Nos. 9-115715 and10-149910). As described above, a ferrite magnet is a ferrimagnetism inwhich the magnetic moments at respective sites of Fe³⁺ are in theopposite directions, and therefore has relatively low saturationmagnetization. However, according to the above-identified laid-openpublications, if ions with a smaller magnet moment than that of Fe areplaced at particular sites of Fe ions, then the number of sites with the“downward” magnet moment will decrease and the saturation magnetizationσ_(s) will increase. Examples of using Nd or Pr instead of La and usingMn, Co or Ni instead of Zn are also described in these publications.

A ferrite magnet with a composition Sr_(1−x)La_(X)Co_(x)Fe_(12−x)O₁₉,which additionally contains La and Co to increase both the coercivityH_(CJ) and saturation magnetization σ_(s) thereof, is disclosed in“Digests of the 22th Annual Conference on Magnetics in Japan” (which wasdistributed on Sep. 20, 1998).

However, even these ferrite magnets cannot exhibit sufficiently improvedcoercivity and saturation magnetization. In particular, if theSr_(1−x)La_(x)Co_(X)Fe_(12−x)O₁₉ compound, in which Fe and Sr arereplaced with Co and La, respectively, is calcined at such a temperatureas that disclosed in Japanese Laid-Open Publication No. 10-149910 (i.e.,1200° C.), then the resultant coercivity is not high enough althoughrather high saturation magnetization σ_(s) is attainable.

An article included in “Digests of the 22th Annual Conference onMagnetics in Japan” (which was distributed on Sep. 20, 1998) reportsthat coercivity would be increased to a certain degree by replacing Fewith Co, not Zn. However, the article does not specify the causes. Inaddition, neither coercivity nor remanence seems to be sufficientlyimprovable.

In view of these respects, a primary object of the present invention isto provide a ferrite magnet powder with saturation magnetization andcoercivity both improved and a magnet made from the magnet powder.

DISCLOSURE OF INVENTION

An inventive magnet powder has a ferrite primary phase represented as(1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO, where x and y represent molefractions and 0.1≦x≦0.4, 0.1≦y≦0.4 and 5.5≦n≦6.5. Fe has a magneticmoment oriented upwardly with respect to a crystal c-axis at a number ofsites thereof, and also has an opposite magnetic moment orienteddownwardly with respect to the crystal c-axis at another number of sitesthereof. And Fe is replaced with Co at the greater number of sitesthereof.

The magnet powder is preferably calcined at a temperature higher than1300° C.

In a preferred embodiment, the magnet powder shows a magnetic anisotropyfield H_(A) of 1750 kA/m (22 kOe) or more and a saturation magnetizationσ_(s) of 84.78 μWbm/kg (67.5 emu/g) or more at room temperature.

An inventive bonded magnet is characterized by containing the magnetpowder. On the other hand, an inventive sintered magnet is characterizedby being made from the magnet powder.

An inventive method for making a magnet powder includes the steps of:preparing a source material blended powder, in which oxide powders of Laand Co are added to powders of SrCo₃ and Fe₂O₃, respectively; calciningthe source material blended powder at a temperature higher than 1300° C.and equal to or lower than 1450° C., thereby forming a ferrite calcinewith the composition of (1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO, where0.1≦x≦0.4, 0.1≦y≦0.4 and 5.5≦n≦6.5; and pulverizing the calcine. Notethat the step of preparing the source material blended powder refers tonot only making such a source material blended powder from thebeginning, but also purchasing and using a source material blendedpowder that was made by others and blending powders prepared by others.

The calcining step is preferably carried out at a temperature equal toor higher than 1350° C.

An inventive method for producing a magnet includes the steps of:preparing a source material blended powder, in which oxide powders of Laand Co are added to powders of SrCo₃ and Fe₂O₃, respectively; calciningthe source material blended powder at a temperature higher than 1300° C.and equal to or lower than 1450° C., thereby forming a ferrite calcinewith the composition of (1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃. yCoO, where0.1≦x≦0.4, 0.1≦y≦0.4 and 5.5≦n≦6.5; pulverizing the calcine to obtain aferrite magnet powder; and, shaping and sintering the ferrite magnetpowder.

Another inventive method for producing a magnet includes the steps of:preparing a source material blended powder, in which oxide powders of Laand Co are added to powders of SrCo₃ and Fe₂O₃, respectively; calciningthe source material blended powder at a temperature higher than 1300° C.and equal to or lower than 1450° C., thereby forming a ferrite calcinewith the composition of (1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO, where0.1≦x≦0.4, 0.1≦y≦0.4 and 5.5≦n≦6.5; pulverizing the calcine to obtain aferrite magnet powder; and forming a bonded magnet from the ferritemagnet powder.

The calcining step is preferably carried out at a temperature equal toor higher than 1350° C. Another inventive magnet powder has a ferriteprimary phase represented as (1−x)A0(x/2)R₂O₃.(n−y/2)Fe₂O₃.yCoO, where Ais at least one element selected from the group consisting of Sr. Ba, Caand Pb; R includes at least one element selected from the groupconsisting of rare-earth elements including Y and Bi; x and y representmole fractions; and 0.1≦x≦0.4, 0.1≦y≦0.4 and 5.5≦n≦6.5. Fe has amagnetic moment orient upwardly with respect to a crystal c-axis at anumber of sites thereof, and also has an opposite magnetic momentoriented downwardly with respect to the crystal c-axis at another numberof sites thereof. And Fe is replaced with Co at the greater number ofsites thereof.

The magnet powder is preferably calcined at a temperature higher than1300° C.

Still another inventive magnet is characterized by being made from themagnet powder.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating the dependence of the saturationmagnetization σ_(s) on the calcining temperature for examples of thepresent invention and comparative examples.

FIG. 2 is a graph illustrating the dependence of the magnetic anisotropyfield H_(A) on the calcining temperature for examples of the presentinvention and comparative examples.

FIG. 3 is a graph illustrating the dependence of the saturationmagnetization σ_(s) and magnetic anisotropy field H_(A) on thesubstitution amount for examples of the present invention andcomparative examples, where x=y.

FIG. 4 is a graph illustrating X-ray diffraction patterns correspondingto respective calcining temperatures of 1200, 1300 and 1400° C. in theexamples of the present invention.

FIG. 5(a) schematically illustrates how Fe is replaced with Co when thecalcining temperature is 1300° C. or less, and

FIG. 5(b) schematically illustrates how Fe is replaced with Co when thecalcining temperature is higher than 1300° C.

BEST MODE FOR CARRYING OUT THE INVENTION

The inventive magnet powder has a magnetoplumbite ferrite primary phaserepresented as (1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO. Part of Sr isreplaced with La by the amount x, where 0.1≦x0.4. Part of Fe is replacedwith Co by the amount y, where 0.1≦y≦0.4. Also, 5.5≦n≦6.5.

When Fe is replaced with Co, the saturation magnetization increases solong as the calcining temperature falls within a normal temperaturerange (i.e., around 1200° C.) However, we observed decrease insaturation magnetization when the calcining temperature was raised to alevel exceeding the normal temperature range.

The present inventors found that if La and Co are added to a sourcematerial blended powder and if the mixture is calcined at a temperaturehigher than 1300° C., then coercivity (i.e., magnetic anisotropy field)can be increased while suppressing the decrease in saturationmagnetization. This is probably because the sites where Fe is replacedwith Co change with the rise in calcining temperature, thus improvingthe magnetic properties. More specific reasons are as follows.

In a magnetoplumbite ferrite with the stoichiometric composition ofSrO.6(Fe₂O₃), twelve Fe³⁺ ions are contained per unit cell. Of theseions, eight Fe³⁺ ions have a magnetic moment upwardly oriented withrespect to the crystal c-axis, while the other four Fe³⁺ ions have amagnetic moment downwardly oriented thereto. In this specification, theorientation of the magnetic moment of the eight Fe³⁺ ions, which arefound at the greater number of sites, is represented as “upward”.Alternatively, this orientation may also be regarded as “downward” andthe orientation of the magnetic moment of the remaining four Fe³⁺ ionsmay, be regarded as “downward”. In the following description, theorientation of the magnetic moment found at the greater number of siteswill be regarded as “upward”.

In partially replacing Fe with Co in such a ferrite, Fe with thedownward magnetic moment would be replaced with Co at a calciningtemperature between 1200 and, 1300° C., both inclusive (FIG. 5(a)). At acalcining temperature higher than 1300° C. on the other hand, Fe withthe upward magnetic moment would be replaced with Co (FIG. 5(b)). Themagnetic moment of Co is smaller in magnitude than that of Fe. Thus, ifFe with the downward magnetic moment is replaced with Co, then thesaturation magnetization of the ferrite will increase. However, if Fewith the upward magnetic moment is replaced with Co, then the saturationmagnetization of the ferrite will slightly decrease but the magneticanisotropy field (i.e., coercivity) will increase sufficiently as shownin FIG. 5(b).

Nevertheless, if the calcining temperature exceeds 1450° C., then thecrystal grains will grow excessively and various inconveniences will becaused. For example, it will take too much time to carry out apulverization process.

Taking these results into account, the calcining temperature ispreferably set to a temperature higher than 1300° C. and equal to orlower than 1450° C. To attain even more enhanced magnetic properties,the calcining temperature preferably falls within a range from 1350 to1450° C.

According to the present invention, excellent magnetic properties areattainable. Specifically, the magnetic anisotropy field H_(A) at roomtemperature exceeds 19×79.58 kA/m (=19 kOe=1512 kA/m) and the saturationmagnetization σ_(s) exceeds 6.5×1.256 μWbm/kg (=66.5 emu/g=83.52μWbm/kg). Also, by controlling the mole fractions (i.e., the amountsreplaced) and the calcining temperature, the magnetic anisotropy fieldH_(A) can be increased to 19.5×79.58 kA/m (=19.5 kOe=1631 kA/m) and to26×79.58 kA/m (=26 kOe=2069 kA/m), while the saturation magnetizationσ_(s) can be increased to 69.2×1.256 μWbm/kg (=69.2 emu/g=86.91 μWbm/kg)and to 67.7×1.256 μWbm/kg (=67.7 emu/g=85.03 μWbm/kg).

According to the present invention, since Fe³⁺ ions in a magnetoplumbiteferrite are replaced with Co²⁺ ions having a different valence, part ofSr is replaced with La to compensate for the difference in valence.Thus, the substitution amount x is preferably approximately equal to thesubstitution amount y. However, the present invention is not limited tothe embodiment where x=y.

Next, an inventive method for making the magnet powder will bedescribed.

First, powders of SrCO₃ and Fe₂O₃(α-ferric oxide) are blended at a molefraction ratio between 1:5.5 and 1:6.5. At this time, La₂O₃, CoO and soon are added to the source material blended powder. The primary grainsizes of SrCO₃, Fe₂O₃, La₂O₃, and CoO powders are about 0.8 μm, about0.5 μm, about 1.0 μm and about 1.0 μm, respectively.

In this manner, La and Co are preferably added as powders of La and Cooxides. Alternatively, La and Co may be added as powders of respectivenon-oxide; compounds, e.g., carbonates, hydroxides or nitrates.

If necessary, any other compound containing SiO₂, CaCo₃, SrCO₃, Al₂O₃ orCr₂O₃ may be added to the powder by about 1% by weight.

The blended source material powder is heated to a temperature between1300 and 1450° C. in the air using a rotary kiln, for example, andsolidified, thereby forming a magnetoplumbite ferrite compound. Thisprocess will be herein called a “calcination process” and the resultingcompound will be herein called a “calcine”. The calcination time ispreferably 1 to 5 hours.

The calcine obtained by this calcination process has a magnetoplumbiteferrite primary phase represented by the following chemical formula:

(1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃ .yCoO

(where 0.1≦x=y≦0.4 and 5.5≦n≦6.5)

and has an average grain size between 1 and 10 μm.

By pulverizing or milling this calcine, the inventive magnet powder canbe obtained.

FIGS. 1 and 2 illustrate the dependence of the magnetic properties onthe calcining temperature for various samples with respectivelydifferent amounts replaced x. In FIG. 1, the ordinate represents thesaturation magnetization, while the abscissa represents the substitutionamount x (=y). In FIG. 2, the ordinate represents the magneticanisotropy field, while the abscissa represents the substitution amountx (=y).

FIGS. 1 and 2 illustrate respective measured values for the samples, ofwhich the amounts replaced x are between 0 and 0.5. The saturationmagnetization σ_(s) and the magnetic anisotropy field H_(A) were bothmeasured at room temperature (23° C.) with an open flux magnetometerusing pulsed magnetic fields. The method of measurement is as follows.

In general, the magnetization curve as defined in an intense magneticfield created by a ferromagnetic or ferrimagnetic is given by

I=I _(s)(1−a/H−b/H ²+. . . )+χ₀μ₀ H

This equation is called a saturation asymptotic formula. The first termis generated because the magnetic moments are not completely alignedwith the direction of the magnetic field due to magneto crystallineanisotropy, for example. The second term represents that the magnitudeof the magnetic moment itself increases with the strength of themagnetic field. In obtaining the spontaneous magnetization I_(s)(σ_(s))experimentally, if the magnetic anisotropy is not particularly large (inthe range from K₁ to 10⁴ J/m³), the term b/H² is almost negligible evenfor a magnetic field H of 10⁶ A/m or more. Thus, as for a magnetic fieldH of 10⁶ A/m or more, I_(s) can be obtained by seeing if the term χ₀H ora/H exists and by extrapolating H and 1/H into zero, respectively.

Also, in a magnetization curve obtained by measuring the properties of acalcined magnetoplumbite Sr ferrite powder with a mole fraction of 6.0(i.e., SrO.6Fe₂O₃), the magnetization I becomes linear when the externalmagnetic field H is 30×79.58 kA/m (=30 kOe=2387 kA/m) or more. Thus, theabove equation will be a linear equation of H in the second term becausethe first term becomes I_(s). Accordingly, by extrapolating H into zero,its y segment is set equal to σ_(s). As a result, the saturationmagnetization of SrO.6Fe₂O₃ was (69.2 ±0.1)×1.256 μWbm/kg. The magneticanisotropy field H_(A) was obtained by measuringsecond-order-differentiated susceptibility using the same pulsedmagnetization measuring apparatus. As a result, H_(A) of SrO.6Fe₂O₃measured 1.43 MA/m (18 kOe).

FIG. 3 illustrates the dependence of the magnetic anisotropy field H_(A)and saturation magnetization σ_(s) on the amounts replaced.

The following points are clear from the graphs shown in FIGS. 1 through3.

1. When La and Co are added, the magnetic properties depend on thecalcining temperature. In particular, the magnetic anisotropy fieldH_(A) greatly depends on the calcining temperature if the substitutionamount x of La and Co is large.

2. If the substitution amount x is 0.1 or more, the magnetic anisotropyfield H_(A) increases up to 18 kOe or more. Also, the higher thecalcining temperature, the more significantly the magnetic anisotropyfield H_(A) increases. The magnetic anisotropy field H_(A) reaches itsmaximum when the substitution amount x is 0.3 (FIG. 3).

3. If the substitution amount x is 0.4 or more, the saturationmagnetization σ_(s) tends to decrease as the calcining temperature rises(FIG. 3).

4. To attain a magnetic anisotropy field H_(A) of 22×79.58 kA/m (=22kOe=1750 kA/m) or more while maintaining the saturation magnetizationσ_(s) at 67.5×1.256 μWbm/kg (=67.5 emu/g =84.78 μWbm/kg) or more, thesubstitution amount x should be between 0.2 and 0.3 and the calciningtemperature should exceed 1300° C.

FIG. 4 illustrates X-ray diffraction patterns for respective calciningtemperatures of 1200, 1300 and 1400° C. Apparently, the diffractionpatterns hardly depend on the calcining temperature. However, as isclear from the data illustrated in FIG. 1, as the calcining temperaturerises, the magnetic anisotropy field H_(A) of the calcine increases.This is probably because the sites where Fe, is replaced with Co changewith the rise or fall of the calcining temperature as described above.

In this manner, by setting the calcining temperature to higher than1300° C. and equal to or lower than 1450° C. and by replacing Fe withCo, the magnetic anisotropy field H_(A) can be greatly increasedaccording to the present, invention while suppressing the decrease insaturation magnetization σ_(s).

Hereinafter, an inventive method for producing a ferrite magnet will bedescribed.

First, a calcine is obtained by the above method. Next, the calcine ispulverized into fine particles by performing a fine pulverizationprocess using vibrating mill, ball mill and/or attriter. The averagegrain size of the fine particles is preferably between about 0.4 andabout 0.7 μm (air transmission method). The fine pulverization processis preferably performed as dry and wet pulverization in combination. Anaqueous solvent such as water or any of various non-aqueous solvents maybe used for the wet pulverization. In the wet pulverization process,slurry is made by mixing a solvent with the calcined powder. Any ofknown surfactants is preferably added to the slurry.

Thereafter, the slurry is pressed within a magnetic field or without amagnetic field while removing the solvent from the slurry. After thepressing, known manufacturing processes of degreasing, sintering,finishing, cleaning and testing are carried out, thereby obtaining afinal ferrite magnet product. The sintering process may be performed inthe air at a temperature between 1200 and 1250° C. for about 0.5 to 2hours. The average grain size of the sintered magnet obtained by thesintering process is between 1 and 1.5 μm, for example.

If the ferrite magnet powder is compounded and cured with flexiblerubber or hard and lightweight plastic, a bonded magnet may also beproduced. In such a case, the inventive magnet powder is mixed andkneaded with a binder and an additive and then molded. The moldingprocess may be injection, extrusion or roll molding.

According to the present invention, the magnetic properties can beimproved by performing the calcination at a relatively high temperatureas described above. It is generally believed that the calciningtemperature should preferably be low (e.g., about 1200° C.) because thehigher calcining temperature will not only make the subsequentpulverization more difficult but also degrade the sinterability.However, according to the present invention, such inconveniences causedby the high calcining temperature are eliminated to set the calciningtemperature at as high as 1300° C. or more. For example, before thepowder is calcined, the powder is crushed finely and further expansionof the grain size is prevented in some way or other. Or coarselypulverized particles are finely pulverized using a roller mill or a rodmill.

It should be noted that Sr may be replaced with at least one elementselected from the group consisting of Ba, Ca and Pb. Also, La may bereplaced with at least one element selected from the group consisting ofrare-earth elements including Y and Bi at least partially.

EXAMPLE

First, a source material powder with a composition represented as(1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO, which was compounded such thatx=y=0.3, was calcined at 1350° C., thereby preparing the inventivemagnet powder.

Next, the magnet powder was finely pulverized to a size of 0.52 μm.Then, CaCo₃=0.7 wt % and SiO₂=0.4 wt % were added to the resultingfinely pulverized powder and blended together. The finely pulverized,blended powder was shaped in a magnetic field and then sintered at 1230°C. for 30 minutes, thereby obtaining a sintered magnet.

The magnetic properties of the resultant sintered magnet were: remanenceBr of 0.44T; coercivity H_(CJ) of 4.6×79.58 kA/m; and (BH)_(max) of4.7×7.958 kJ/m³.

Industrial Applicability

According to the present invention, calcine and magnet powder can havetheir saturation magnetization and coercivity both improved at the sametime. Thus, a magnet with excellent magnetic properties can be producedin accordance with the present invention.

What is claimed is:
 1. A magnet powder with a ferrite primary phaserepresented as (1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO, wherein x and yrepresent mole fractions, and wherein 0≦x≦0.4, 0.1≦y≦0.4 and 5.5≦n≦6.5,and wherein Fe has a magnetic moment oriented upwardly with respect to acrystal c-axis at a number of sites thereof, and also has an oppositemagnetic moment oriented downwardly with respect to the crystal c-axisat another number of sites thereof, and wherein the number of sitesoriented in one direction is greater than the number of sites orientedin the opposite direction and Co substitutes for Fe in sites which havea greater number, and wherein said magnet exhibits a magnetic anisotropyfield H_(A) of 1750 kA/m or more and saturation magnetization σ_(s) of84.78 μWbm/kg or more at room temperature.
 2. A bonded magnet containinga magnet powder as recited in claim
 1. 3. A sintered magnet made from amagnet powder as recited in claim
 1. 4. A method for making a magnetpowder, comprising the steps of: preparing a source material blendedpowder, in which oxide powders of La and Co are added to powders ofSrCo₃ and Fe₂O₃, respectively; calcining the source material blendedpowder at a temperature higher than 1350° C. and equal to or lower than1450° C., thereby forming a ferrite calcine with the composition of(1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO, where 0.1≦x≦0.4, 0.1≦y≦0.4 and5.5≦n≦6.5; and pulverizing the calcine.
 5. A method for producing amagnet, comprising the steps of: preparing a source material blendedpowder, in which oxide powders of La and Co are added to powders ofSrCo₃ and Fe₂O₃, respectively; calcining the source material blendedpowder at a temperature higher than 1350° C. and equal to or lower than1450° C., thereby forming a ferrite calcine with the composition of(1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO, where 0.1≦x≦0.4, 0.1≦y≦0.4 and5.5≦n≦6.5; pulverizing the calcine to obtain a ferrite magnet powder;and shaping and sintering the ferrite magnet powder.
 6. A method forproducing a magnet, comprising the steps of: preparing a source materialblended powder, in which oxide powders of La and Co are added to powdersof SrCo₃ and Fe₂O₃, respectively; calcining the source material blendedpowder at a temperature higher than 1350° C. and equal to or lower than1450° C.,thereby forming a ferrite calcine with the composition of(1−x)SrO.(x/2)La₂O₃.(n−y/2)Fe₂O₃.yCoO, where 0.1≦x≦0.4, 0.1≦y≦0.4 and5.5≦n≦6.5; pulverizing the calcine to obtain a ferrite magnet powder;and forming a bonded magnet from the ferrite magnet powder.
 7. A magnetpowder with a ferrite primary phase represented as(1−x)AO.(x/2)R₂O₃.(n−y/2)Fe₂O₃.yCoO, wherein A is at least one elementselected from the group consisting of Sr, Ba, Ca and Pb, and wherein Rincludes at least one element selected from the group consisting of:rare-earth elements including Y and Bi, and wherein x and y representmole fractions, and wherein 0.1≦x≦0.4, 0.1≦y≦0.4 and 5.5≦n≦6.5, andwherein Fe has a magnetic moment oriented upwardly with respect to acrystal c-axis at a number of sites thereof, and also has an oppositemagnetic moment oriented downwardly with respect to the crystal c-axisat another number of sites thereof, and wherein the number of sitesoriented in one direction is greater than the number of sites orientedin the opposite direction and Co substitutes for Fe in sites which havea greater number, and wherein said magnet exhibits a magnetic anisotropyfield H_(A) of 1750 kA/m or more and saturation magnetization σ_(s) of84.78 μWbm/kg or more at room temperature.
 8. A magnet made from amagnet powder as recited in claim 7.